The present invention relates to wind-propelled vehicles, and particularly to such vehicles including soft wing-sails for propelling the vehicle, such as described in my prior U.S. Pat. Nos. 6,863,008 and 7,603,958, the contents of which are incorporated herein by reference.
In order to have a wing-sail effective in all wind directions, the wing-sail has to rotate towards the wind direction and to maintain the proper angle of attack. This can be achieved by using a free standing and rotating mast that supports, and is secured to, the wing such that the wing and the mast rotate together towards the wind.
Free standing masts in large boats encounter two problems: when large masts are in use, free standing and rotating masts need extensive reinforcement in order to take all the loads of the wing-sails, as well as to prevent the mast from bending, both caused by the movement of the boat in the open sea; the result is a large diameter and wall thickness mast that is heavy and expensive. When large, soft wing-sails are made of sailcloth wrapped around the mast, the sailcloth is divided into three different sail panels, which generally require mounting tracks for each of the sail panels both sides of the mast, and special spreaders for slidably mounting the wing-sail on the tracks; see, for example, my above-cited U.S. Pat. No. 7,603,958.